Seismic Tomography of Fault Zones

Seismic tomography of fault zones employs the propagation of P and S waves to image the subsurface structure and mechanical properties of faults and surrounding damage zones. By inverting travel times, amplitudes and waveform attributes, researchers obtain high-resolution three-dimensional models of seismic velocity, attenuation and anisotropy that reveal the distribution of fractures, fluid saturation and mechanical heterogeneity. Fault zones commonly exhibit low-velocity zones associated with fractured and fluid-filled rock, and high-velocity asperities which may accumulate stress and control earthquake nucleation. Recent advances integrate ambient noise cross-correlation, dense nodal arrays, geodetic observations and adjoint-state inversion techniques to improve resolution across a broad range of scales, from shallow damage bands of tens to hundreds of metres to seismogenic depths of tens of kilometres. These images elucidate variations in fault rheology, slip behaviour and seismic hazard potential, offering critical inputs for rupture dynamics models and risk assessment. The global application of seismic tomography spans major plate-boundary faults and intraplate regions, informing our understanding of fault evolution and enabling the identification of prospective sites for large earthquakes. High-resolution tomography supports improved forecasting of rupture propagation paths, assessment of aftershock distributions and the design of effective mitigation strategies in urban and offshore environments.

Research from Nature Portfolio

Recent studies have applied improved double-difference inversion methods to generate three-dimensional velocity models around large historical earthquakes in the Northeastern Tibetan Plateau. High-velocity anomalies extending to mid-crustal depths were interpreted as robust asperities that concentrate tectonic stress over long periods of locking. These velocity-derived asperities correlate closely with the locations of major rupture initiation and suggest that regions of elevated mechanical strength play a pivotal role in controlling earthquake nucleation. The workflow integrates abundant regional seismic arrivals with rigorous error minimisation to achieve kilometre-scale resolution, marking a significant step towards predictive assessments of seismogenic potential along mature faults.

Seismic Tomography of Fault Zones publication trend

The graph below shows the total number of articles in seismic tomography of fault zones across all publications each year (not limited to Nature Index journals).

Technical terms

Seismic tomography: Inversion of seismic wave travel times and amplitudes to construct three-dimensional models of subsurface elastic properties.

Fault damage zone: The fractured and mechanically weakened region surrounding the core of a fault, often characterised by reduced seismic velocities.

Asperity: A region of locally elevated seismic velocity and mechanical strength on a fault that can concentrate stress and act as an earthquake nucleation site.

Ambient noise imaging: Tomographic technique using cross-correlations of continuous seismic noise to extract surface wave information for subsurface structure mapping.

Adjoint-state tomography: An inversion method employing the adjoint of the wave equation to compute sensitivity kernels, enabling travel-time tomography without explicit ray tracing.

References

1. Constraining Fault Damage Zone Properties From Geodesy: A Case Study Near the 2019 Ridgecrest Earthquake Sequence. Geophysical Research Letters (2023).
2. Shallow three-dimensional structure of the San Jacinto fault zone revealed from ambient noise imaging with a dense seismic array. Geophysical Journal International (2018).
3. Structure-controlled asperities of the 1920 Haiyuan M8.5 and 1927 Gulang M8 earthquakes, NE Tibet, China, revealed by high-resolution seismic tomography. Scientific Reports (2021).
4. Adjoint-state differential arrival time tomography. Geophysical Journal International (2023).
5. General Seismic Architecture of the Southern San Andreas Fault Zone around the Thousand Palms Oasis from a Large-N Nodal Array. The Seismic Record (2022).